Nanostructure Modified Gas Sensor Detection Matrix for NO Transient Conversion of NO to NO2

Abstract

Porous silicon (PS) conductometric gas sensors are used to create asensitivity matrix for the room temperature detection of NOx (NO, NO2).``P-type{''} nanopore coated microporous silicon is treated with tin,nickel, copper, and gold, electrolessly deposited onto the PS surface toform SnOx, NiO, CuxO, and AuxO nanostructured centers as confirmed byXPS measurements. The relative sensitivities of these modified PS gassensor surface sites have been measured under 1-5 ppm NO exposure. Animproved sensitivity of up to 10 times that of untreated PS is observedfor a 1 ppm exposure. The choice of deposits is based on the hard tosoft acid character of the nanostructured metal oxide islands that arefractionally deposited on the semiconductor interface and their effecton the physisorption of NO, a weak base, dictated by an inverse pattern(IHSAB) to the hard-soft acid base concept. NO, a free radical, caninteract with oxygen sites on the modified PS sensor interfaces, toeffect a transient NO2 signal unique to PS-based NO sensors, which isnot observed as other basic analytes including NH3, PH3, H2S, SO2, andCO interact with ``p-type{''} PS. A comparison is made between thecurrent PS sensor systems which operate at room temperature andelectrochemical and traditional metal oxide sensors. (C) 2011 TheElectrochemical Society. {[}DOI: 10.1149/1.3583368] All rights reserved.